Glow discharge oven



Dec. 23, 1941. B BERGHKASVET'AL 2,266,735

GLOW DISCHARGE OVEN Filed March l1, 1940 a Vacuum Space.

Patented Dec. 23, 1941 Grow DISCHARGE ovEN Bernhard Berghaus, Berlin-Lankwitz, and Wilhelm Burkhardt, Berlin-Grunewald, Germany; said Burkhardt assigner to said Berghaus Application March 11, 1940, Serial No. 323,452

In Germany March 11, 1939 6 Claims.

The present invention relates to glow discharge ovens or furnaces and more particularly pertans to the cathode structure of such apparatus.

The fact that heat is generated with a glow' discharge is known and it is also known that such heat may be utilized for the heating of objects. The heretofore known processes or devices have not succeeded in gainingA a foothold in practice, since not only the extent of their performance, but also the efliciency and in particular the operating reliability resulted in values quite useless in practice. j

The invention relates to a glow discharge oven characterized by the feature that the cathode is provided with spaced screening plates. This results in the advantage that the cathode becomes heated and may be made to reach glow temperatures. The cathode in this case advantageously forms an uninterruptedly radiating heating element. The invention consists further of the feature that the glow discharge is formed at a cathode which may be heated by loss heat and is arranged on a cooled carrier with interposition of The interspace may be provided by radiation screens with as large or as small a distance between them as may be desired, so as to maintain the heat current from the heated cathode to the cooled carrier as small as possible. The carrier which is also carrying the cathodical potential, is protected against the discharge of gas by being screened. OI special advantage is the designing of the cathode in such a manner that it forms the inner wall of the oven surrounding the object to be heated at all sides. Behind this cathode is then arranged, suitably distanced and with or without the interpostion of radiation screens,. the water-cooled casing of the oven. The introduction oi the opposing electrode is effected observing special protective measures with respect to insulation, which must be protected against the destructive attack of the gas discharge. To the insulation is preferably pre-arranged a protective space, between the current path and the oven casing, spaced in such a manner that an independent discharge cannot take place therein.

It has been found that, for instance, at a water-cooled cathode a gas discharge is divided in two energy components. One part, being due to the ion stream, passes as loss heat into the cooling water, the other part, being due to the electron current, is employed as useful output within the oven. A satisfactory relation between the useful output and the loss can only be attained with an appreciable load on the cathode measured in watts per square centimeter. Hence, such oven'willy show usable efiiciency only after a certain high load on the cathode surface has been reached. This arrangement is particularly suited for the rapid heating of objects and for generating any desired high temperatures, but will be uneconomical for prolonged maintenance of the final temperature attained.

It has further been found that. the division of the energy current is increasingly shifted in favor of the electron current when heating the cathode. Heating the cathode may be effected by the loss heat of the ion stream. The object to be heated having reached a temperature resulting in a noticeable output of energy by radiation, the cathode is heated not only by the loss heat, but additionally by the radiation energy of the hot body, having an additional favorable influence on the division of the supplied output in an economic respect, since by this the cathode is separately heated additionally. It has further been found that with increasing temperature of the cathode the stability of the gas discharge is extraordinarily increased. Glow temperatures of the cathode having been reached, cleaning thereof of adhering foreign bodies, such as oxides, fats and other foreign matter will take place automatically. This fully ensures service reliability a's compared with cold cathodes.

Radiation screens may be arranged behind the hot cathode for the purpose of decreasing the energy current passed to the cathode by radiation, These radiation screens represent heat insulation, having an extremely low heat capacity. The design of the radiation screens with respect to the condition of their surface and the choice of the material, and their number, will be based on the well-known thermic relations. Hence, the described oven is a vacuum oven, whose heating element, with a most favorable arrangement, represents a uninterruptedly radiating surface with the resulting advantage, that the object or crucible to be heated assumes a temperature even exceeding that of the heating element. The insulation of the oven has so small a heat capacity that its heating to maximum temperature will take place in the shortest time imaginable, it being possible to heat with any desired high output almost immediately after having been switched on.

.An object of the invention resides in providing means for creating one or more narrow protecting gaps or spaces adjacent the cathode in a glow discharge furnace.

Another object of the invention includes one or more screen plates adjacent the cathode of a glow dischargefurnace wherein the plates are spaced with respect to each other and with respect to the cathode so as to form spaces therebetween of such narrow dimensions that the glow discharge within the furnace chamber is prevented from extending into the spaces between the screening plates and one of the plates and the cathode.

Other and further features and objects of the invention will be, apparent from consideration of the accompanying drawing and the following description wherein an exemplary embodiment of theinvention is disclosed. Y

The single figure of the drawing is asectional view of a glow discharge furnace embodying the-invention.

The glow discharge'oven'consists of a lower part i and a removable upper part 2, both being connected as cathode and between which is arranged a packing. In the lower part is arranged'an anode 4, insulated and screened by a protective space 3.

The upper part 2 is provided with a jacket 5 which, as needed, may be cooled or evacuated. According to the invention there are arranged in the upper part one or several mantles 6, 1, t

vin such a manner that between them and the wall of the oven remain one or several narrow spaces I9, 20, 2|, ranging between 0.1 and 5 millimeters in width, being in connection with the evacuated inner space and being so narrow that no glow discharge can take place therein.

A cooling agent may be conductor to the hollowv current passageA through the conduit 9 and discharged through the connecting piece I0.

Parts II, I2, I3 are insulating and packing rings. Part I4 is a press-on ring. The vacuum pump is connected to the pipe I6, provided with a sieve I5 for retainingthe discharge. Through a similar second pipe (not shown) is admitted the filling as, for example, hydrogen in regulated quantities,-so that a pressure of about 5 to 0.01 millimeters of mercury is maintained inthe oven,

while the pipe Il is serving for accommodating a thermo couple. Part I0 is an inspection glass screened by a space 22.

What is claimed is:

I l. In a glow discharge furnace, a sealed housing providing a cathode, means for supporting articles to be heated within the housing, and means covering the inner surface of the cathode and spaced therefrom to provide a relatively narrow gap adjacent the cathode.

rality of screening plates covering the inner surface of the cathode, said plates being spaced with* respect to each other and with respect to the cathode to provide a plurality of gaps adjacent the cathode.

4. A glow discharge furnace according to claim 1 wherein said means is spaced from the cathode at a distance between 0.1 and 5 millimeters.

5. A glow discharge furnace according to claim 3 wherein the gaps between said plates are in open lcommunication with the interior of the housing.

6. In a glow discharge furnace, a sealed housingproviding a cathode, means for supporting articles to be heated within the housing, a jacket c surrounding the' housing for receiving a cooling medium, and a casing within the housing covering .the inner surface thereof and spaced from BERNHARD BERGHAUS. WILHELM BURmIARDT. 

